ASTRONOMY 340

FALL 200725 September 2007

Class #6-#7

Review

Physical basis of spectroscopy Einstein A,B coefficients probabilities of transistions

Absorption/emission coefficients are functions of ρ, N, quantum mechanical factors, temperature

Molecular spectroscopy More available quantum states – rotational, vibrational

Low energy transitions IR, radio part of the spectrum (hν << kT)

Examples CaI in the atmosphere of Mercury linewidth = Δλ = Δv

(1/2)mv2 = (3/2)nkT

Quantum mechanics

Principle quantum # (n) energy

Angular momentum, l

Spin, s

Multi-electron atoms have many filled orbitals

(constrained by exclusion principle) e.g. electron

with n=2 could have l=1 or l=0, and if its l=1 it

could have s=1/2 or -1/2 many orbitals, many

transitions, many spectral lines

http://physlab2.nist.gov/PhysRefData/ASD/lines_form.html

Molecules

Nuclei act as single nucleus with common potential

Multiple nuclei generate other quantum states

Electronic

Rotational

Vibrational low energy radio/NIR part of the

spectrum

Most surface and atmospheric components are

molecular

CO

Main product of stellar evolution

Transitions easily excited rotational modes

J = 1 0 (2.7mm, 115.3 GHz)

J = 2 1 (1.3mm)

Observations radiotelescopes

Measure “brightness temperature”, Tb

Optically thick vs optically thin

Mars – non thermal CO

Example: Mercury

What does the spectrum of Mercury look like?

Planetary reflectance spectrum

Terrestrial emission and absorption

Narrow source emission lines wavelength shifted via

Doppler

Process

What do you actually measure?

Linewidths?

Wavelength?

Spencer et al. 2000

Science 288, 1208

Io is the most geological

activity of anything in

solar system volcanoes

discovered during

Voyager flyby in ’79

What’s coming out of that

volcano?

Spencer et al. 2000

Science 288 1208

Use transit of Io across Jupiter to observe plumes from volcanoes why?

Scattered light dust scatters photons effectively so you get a “non-thermal” continuum effect is to fill in absorption line

Identify S2 and SO2 lines in 240.0-300.0nm range -> fit linewidths

T ~ 300 K

N(SO2) ~ 7 x 1016 cm-2

N(S2) ~ 1 x 1016 cm-2

Pure SO2 suggests a lack of Fe since Fe will bind with SO2 if available

CO molecule

C,O main products of stellar evolution, particularly intermediate mass stars 3He 12C or 12C + 4He 16O

On terrestrial planets CO comes from CO2 + uv photons CO + O

Transitions J = principle rotational quantum number

J=10 (2.7mm, 115.3 GHz)

J=21 (1.3mm), J=32 (0.87mm)

J=0 is ground state, but get to J=1 if there’s ambient thermal bath with T~5.5K it’ll get excited to J=1 level

CO molecule

Photons too dang weak for CCDs, so you need a radio telescope

Characterize intensity with a “brightness temperature” if line is optically thick the observed brightness temperature really is the thermal temperature Tb = (λ2/2k)Bλ

Rewrite radiative transfer as:

(dTb(s)/dτλ) = Tb(s) – T(s)

Tb(s) = Tb(0)e-τ(s) + T(1-e-τ(s))

Tb = τT (τ << 1)

Tb = T (τ >> 1)

Venus Images in J=1-0 Line

Observations

2.7mm continuum, J=1-0 CO line

3-element interferometer

Continuum results

10% increase in Tb from day side to night side a change in

atmospheric conditions?

CO line results

Line shape varies broad, shallow lines on dayside; deep,

narrow lines on night side

Note on Conductivity

Specific heat units are J mole-1 K-1 function of

temperature for most minerals

Example: feldspar (KAlSi3O8)

Transition Slide….

Radiative transfer tells us how radiation is affected

travelling through some substance (gas)

In Rayleigh-Jeans approximation we can substitute

a temperature (Tb) for the radiation intensity

Now onto some fun stuff – planetary surfaces….

Relevant reading:

Chapter 5

Processes at Work

Impact cratering

Weathering/erosion

Conditions of the atmosphere

Geological activity

Volcanic activity

Tectonics

Geological activity - Earth

Volcanism Shield volcanoes

Formed via a single plume

Hawaii – crustal plate moving over a hot spot

“cone” volcanoes

Formed over subduction zones

Cascade mountains, Mount Etna

Earthquakes At plate boundaries

Plate tectonics Mid-ocean ridges, mountain chains, moving continents,

earthquakes, “ring of fire”, global resurfacing

Apollo 17 View of Earth

Earth Topographic Map

Mercury

Heavily cratered

No volcanoes, no mountain chains, no plate

boundaries, no continents no recent tectonics

Shrinking?

Weak magnetic field

Conclusion: one plate planet with no activity over

the past several billion years; surface is shaped by

impacts

Mercury, Mariner 10 3/74, 9/74, 3/75

Mercury

South Pole

Mercury, Scarp

displacement

Luna, near side

LUNA

Earth Facing Side The far side

Moon from Galileo Spacecraft

Apollo 14

Apollo 12

Apollo 15

Apollo 17

Apollo 11

Apollo 16

Lunar Highlands

Lunar Mare

Venus

Lots of volcanic activity in the recent past

Characteristic feature is a “coronae” which is a circular structure like the caldera of a volcano but without the mountain to go with it

Global resurfacing about 300 Myr ago

Crater density (number per km2)

We call this a “young” surface

A couple of continent-like features

No obvious plate boundaries

Venus Clouds Mariner 10

Venus Topography identified

Venus Surface, Venera 13

Sapas Mons

Maat Mons

Terrestrial Planet Surface Morphology (4)

• Mars

• Massive Shield Volcanoes

• Huge Erosion Channels

• Much Cratering, much eroded

• Polar Caps

Mars Hubble

Mars Orbiter Laser Altimeter Topographic Map

Sojourner at Yogi Seeds Fig 23-15)

Vallis Marineris (Seeds Fig 23-17

Olympus Mons Viking 1

MOLA Generated Perspective of O.Mons

Vallis Marinaris

Fig 23-22a

Fig 23-23a

Fig 23-23b

Water in Newton Crater, Context

“Evidence” for recent liquid flow

Fig 23-24a

Famous Viking 1 Face

MGS view of the “Face”

Let’s put it all together….

Calculate the surface area to mass ratio (km2 g-1)

Moon: 5.16 10-19

Mercury: 2.26 10-19

Mars: 2.25 10-19

Venus: 9.46 10-20

Earth: 8.55 10-20